1. Field of the Invention
This invention relates to an internal combustion engine which is provided with a main combustion chamber and a pre-combustion chamber to thereby permit the use of a lean mixture for the engine.
2. Description of the Prior Art
Hitherto, it is known to increase the fuel air ratio for a mixture to be supplied to an engine in an attempt to burn the lean mixture, thereby reducing the amounts of harmful gas components contained in exhaust gas from an internal combustion engine, such as carbon monoxide (CO), unburnt hydrocarbons (HC) and nitric oxide (NO.sub.X). However, such lean mixture presents not only poor ignitability but also retarded combustion rate, thus impairing the efficiency of the engine as well as fuel consumption rate (g/ps.hr).
Known as one of the solutions to this problem is an internal combustion engine which is provided with a main combustion chamber and a pre-combustion chamber. The combustion chamber of the engine of this sort is divided into a main combustion chamber and a pre-combustion chamber which is communicated by a passage with the main combustion chamber, whereby a mixture introduced into the pre-combustion chamber is first ignited, after which the flame within the pre-combustion chamber is discharged into the main combustion chamber at a high speed through the passage, due to the increase in pressure resulting from the combustion of the mixture in the pre-combustion chamber. This causes to rapidly burn the mixture in the main combustion chamber to increase the combustion rate of the mixture within the main combustion chamber and, prevent the decrease in the efficiency of an engine.
However, such an attempt is plagued with another shortcoming in that, for achieving the aforesaid effects, the cross sectional area of said passage should be reduced to some extent, so that there results insufficient scavenging of the post-combustion gas from the pre-combustion chamber during the suction stroke, thus leaving residual post-combustion gas in the pre-combustion chamber. The residual post-combustion gas therein is compressed during the compression stroke of the main combustion chamber, and thus dilutes the mixture which is introduced from the main combustion chamber into the pre-combustion chamber. This apparently results in difficulties in ignition of the mixture within the pre-combustion chamber by means of the ignition plug. To overcome this shortcoming, there have been proposed an attempt disclosed in SAE Paper No. 700491 eddited by SAE, in which a fuel injection nozzle is provided within the pre-combustion chamber to thereby provide a rich mixture therein, because of its good ignitability, and another attempt in which a subsidiary intake valve for admitting a mixture in the pre-combustion chamber is provided for the pre-combustion chamber, whereby a rich mixture, which is readily ignitable, is introduced through the subsidiary intake valve into the pre-combustion chamber. With those attempts, however, it is mandatory to supply two kinds of mixture having different fuel air ratios, with the results of complicated fuel supply system as well as difficulties in controlling fuel supply. In addition, this increases the manufacture cost of an engine.